The present invention relates to internal voltage set circuits for semiconductor memory devices. In particular, the present invention relates to voltage reset circuits and methods for a semiconductor memory device, using option fuse circuits.
Semiconductor memories include microscopic electronic components often used in digital logic systems, such as computers, or applications based on microprocessors, which are widely used in fields from commercial electronic apparatuses to artificial satellites. Therefore, the evolution of technology in fabricating semiconductor memory devices, for higher integration density and faster operation speed, is helpful to establishing a standard of performance for other digital logic systems.
Semiconductor memories are generally classified into volatile and nonvolatile type memory devices. Volatile memories generally are only able to store and read data when power is supplied and then lose their data if power is suspended or interrupted. In contrast, nonvolatile memories, such as mask read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), and so on, are generally able to retain their data even without application of a power supply. Among nonvolatile memories, flash memories are often employed in computers and memory cards where the ability to electrically erase the memory may be beneficial.
A flash memory is typically operable in three operation modes, including programming, erasing, and reading, using voltages having a level higher than a power source voltage in order to conduct some or all of its operations. Such high voltages are usually generated in the flash memory, because direct supply of high voltages from external to the memory may cause malfunctions or even destruction of elements, such as transistors, due to an electric field induced therein. Thus, the flash memory generally uses internally generated high voltages in light of threshold or breakdown voltage characteristics typically found in transistors. A charge pump is a typical element for generating a high voltage from a low voltage in a flash memory device. A high voltage generated from the charge pump is usually regulated to a predetermined static voltage level by a voltage regulator.
Although flash memory chips have been manufactured by way of the same processing steps under the same conditions as other types of memory, there may be errors on the static voltage levels generated in the chips. Errors of static voltage levels by chip products are usually adjusted to desired levels through test operations before shipment. Such adjustments for voltage levels are typically carried out by means of option transaction modes.
Conventional techniques for option transaction include bonding option, metal option, and fuse option. Among them, the fuse option modes, repairing abnormal voltage levels arising from the procedure of fabrication so as to recover normal voltage levels, are often employed in flash memory products. The fuse option modes may be differentiated into laser and electrical cutting types based on the mechanism used for cutting fuses. The laser cutting mode generally blows a fuse by irradiating a laser beam thereon, while the electrical cutting mode usually blows a fuse by passing an excessive current flow therethrough.
As fuses that have already been cut off cannot typically be recovered to their original states of connection, it is typically impossible to readjust voltage levels after once adjusting the voltage levels by a one-time fuse cutoff. For example, even when there is a mistake on a voltage level once adjusted by fuse cutoff during a former test operation or a need of resetting a voltage level that has been once corrected, it is generally impossible to resume the programming of a fuse option on the characteristics of fuses. As a result, a semiconductor memory product, even though it may have no trouble in operating some functions, may be rendered defective because the readjustment of voltage levels thereof is no longer possible.